This invention relates to subsea wells and is specifically directed to a system whereby an exploratory well can be made into a production well through the use of a retrievable permanent guide base and a conventional latching profile near the upper end of a wellhead housing.
The conventional method of drilling a subsea well utilizes a temporary guide base which is lowered to the sea bed and through which a hole is drilled. The guide wires provide guidance for the drill string and drilling assembly, and guidance for subsequent tools and equipment. Typically the hole is 36" in diameter to accommodate a 30" wellhead housing and a string of 30" casing connected thereto. This 30" wellhead housing is sometimes referred to as the low pressure wellhead housing. Once this hole is drilled to the desired depth, a permanent guide base, together with the 30" wellhead housing clamped thereto, and the desired length of 30" casing, is lowered through the water and the permanent guide base is landed on the temporary guide base.
The permanent guide base is conventionally provided with a gimbal which engages a conically shaped landing ring in the temporary guide base as a means for aligning the permanent guide base horizontally.
The permanent guide base is also provided with vertical posts to provide guidance for subsequent tools and equipment and cooperates with guidelines on the temporary guide base.
After the permanent guide base is positioned on the temporary guide base, the 30" housing is then cemented in place.
The U.S. Pat. No. 4,387,771 of Darrell Jones entitled "Wellhead System for Exploratory Wells" discloses one system of converting an exploratory well to a production well through the use of a separate profile ring which is supported from the wellhead housing and, in turn, supports the wellhead, often termed the high pressure wellhead. This high pressure wellhead typically has an internal diameter of 16 3/4 or 183/4, inches. Subsequent production apparatus, such as the production tree or a conductor riser, may be connected to this profile ring. The profile ring for a nominal initial investment extended the capabilities of the existing system for converting an exploratory well into a production well.
Whether the system of the Jones patent is used, or whether the systems existing prior to the Jones patented system are used to convert the exploratory well into a producing well, the permanent guide base remained subsea and had to be dealt with.
It is an object of this invention to provide a system by which an exploratory well can be converted to a producing well by retrieving the permanent guide base and replacing the same with a completion guide base containing the necessary equipment for producing from the well.
It is apparent that the system of this invention allows the retrieved permanent guide base to be used again and again resulting in considerable cost savings.